Catalysts comprising an alumina carrier, a group VIII noble metal (usually platinum), and rhenium as additional metal promoter (U.S. Pat. No. 3,415,737) are known for their impact in the field of catalytic reforming or aromatic hydrocarbon production. Other catalysts are also known in this field which contain, in addition to a group VIII noble metal (usually platinum) a metal promoter consisting for example of tin, lead, indium, gallium or thallium (U.S. Pat. No. 3,700,588, U.S. Pat. No. 2,814,599).
From tests and after very long periods of use, for example of about one year, it appeared that a platinum-rhenium catalyst is very stable but does not give a maximum selectivity to high grade gasolines. Conversely, platinum-tin or platinum-indium or platinum-thallium catalysts provide for an excellent selectivity but these catalysts suffer from poor stability.
Hence, it seemed advisable to use catalysts containing, in addition to platinum, both promoters simultaneously, e.g. rhenium and tin (U.S. Pat. No. 3,702,294) or rhenium and indium. But it appeared that the selectivity of this type of catalyst was lower than that obtained with a platinum-tin or platinum-indium or platinum-thallium catalyst and also that the stability of this catalyst was less than that of the platinum-rhenium catalyst.